6

Microkeratomes

Rasik B Vajpayee, Namrata Sharma

A microkeratome is the basic instrument required to create a uniform and a homogeneous corneal flap by cutting across the stromal corneal lamellae. The cutting action of microkeratome is derived from a blade, which is powered by an electromechanical system (or turbine system). The microkeratome motor is powered through a cable and activated by a foot pedal control.

An ideal microkeratome should be simple to assemble and operate, easy to clean and reassemble or readily disposable, allow visibility of the cornea during creation of the flap and demonstrate dependability, durability and repeatability in several consecutive cases.

A number of different microkeratomes have been developed by various scientists around the world and are available for clinical use (Tables 6.1 and 6.2). The following section gives a brief description of the various microkeratomes used for LASIK.

Barraquer Microkeratome

Jose Ignacio Barraquer1,2 designed the original microkeratome that served as the basis for the development of all subsequent microkeratomes. Barraquer’s original microkeratome consisted of a head with a steel blade that was passed manually over the cornea. The system had a blade, a thickness plate, which allowed the surgeon to set the depth of the lamellar cut, and a suction ring, which helps in fixing of the eyeball and raising the intraocular pressure (IOP) to facilitate creation of the corneal flap.

Automated Corneal Shaper

Automated Corneal Shaper (ACS) (Fig. 6.1) was designed by Luis Ruiz and marketed by Baush and Lomb Surgicals. The microkeratome head has three gears on one side and is driven by an electric motor which is present in its handle at the rate of 8000 rpm. A stopper mechanism limits the complete run of the microkeratome along the track. The depth of the corneal cut is controlled by the thickness plate that is fitted in the designated groove, on the anterior portion of shaper head. The suction ring is available in various sizes (upto 9.0 mm)

Microkeratomes 55

Figure 6.1. Automated corneal shaper

Two separate foot pedals are supplied with the control unit—a suction pedal and a power pedal. To initiate and maintain the suction, simply depressing and releasing the suction pedal activates the suction pump. After the completion of the LASIK procedure, the suction is disengaged and the pneumatic ring released by pressing and releasing the suction pedal for a second time. The power pedal has two parts -one to activate and advance the microkeratome across the cornea to create the corneal flap, and the other to reverse the microkeratome after the completion of the corneal cut.3

Hansatome

The Hansatome is a four-piece unit (Figs 6.2a to 6.2e), which is being marketed by Baush and Lomb Surgicals. It is a device that further refines the ability of the ACS devised by Ruiz and is currently a popular microkeratome for LASIK surgery.4

The body of the instrument has a gear system engaging over a curve rail track placed laterally in

Figure 6.2a. Hansatome suction ring assembly

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Figure 6.2b. Hansatome console

Figure 6.2c. Microkeratome heads 160 µm and 180 µm

Figure 6.2d. Suction rings 8.5 µm and 9.5 µm

the ring. The displacement over it is guided by the same motor that handles the cutting blade. The microkeratome head has a fixed depth plate and a permanent non-adjustable stop device. It utilizes a disposable metal blade, which comes with an integrated plastic holder. The blade oscillates at a

Microkeratomes 57

Figure 6.2e. Hansatome blade being assembled

speed of 8000 revolutions per minute and is inclined at an angle of 26 degrees.

The unit has two suction rings (8.5 mm and 9.5 mm) that have an elevated, curved gear rack that aligns with the single gear of the Hansatome. It creates a superiorly placed hinge at 12 O’ clock position. Three heads with fixed thickness plates are provided which cut flaps of preset thickness 160 µm, 180 µm and 200 µm. There is a left/right eye adapter that fits over the microkeratome head and the motor is positioned vertically, which enables the microkeratome head to pass over the suction ring on an elevated track away from the speculum and the eyelids. The cutting action of the microkeratome does not start until the appropriate vacuum level is reached and the cutting stops if the vacuum falls below a certain level.

Newer design of the Hansatome microkeratome with a zero-compression head reduces the occurrence of postoperative epithelial defects. Smaller diameter rings are now also available allowing easier access to deep-set eyes.

Moria LSK Carriazo-Barraquer Microkeratome

This is a popular keratome currently in use by many LASIK surgeons. The hand piece and the blades, both are made up of stainless steel (Fig. 6.3). The functioning of this microkeratome may be manual or automated.

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Figure 6.3. Moria Carriazo-Barraquer microkeratome reusable

The steel blade makes 14,000 oscillations per minute and advances at the rate of 3.7 mm/second. The blade angle is 30 degree. It can cut flap diameters ranging between 7 mm and 10.5 mm. The flap depths can be of 160 µm or 180 µm. A variable flap orientation is possible with this microkeratome. The automated machine works through an electric motor while the manual keratome functions on the nitrogen gas turbine.

Recently the original Carriazo-Barraquer system has been modified so that the system is disposable, the blades are reusable without the gears in the head (Fig. 6.4). This Carriazo-Barraquer −2 microkeratome can be used manually or automatically.

Figure 6.4. Moria Carriazo-Barraquer microkeratome single use

Moria One

This manual microkeratome is made of stainless steel and is gearless (Fig. 6.5). A nitrogen turbine yielding high torque and speed of 15,000 revolutions per minutes or 30,000 blades oscillations per minute powers these units. The power unit has two vacuum

Microkeratomes 59

pumps so that the second pump acts as a back up and becomes automatically on, when it detects that the first one has failed. It has a one piece pre-assembled head so that the risk of pre-surgical assembly of the device is obviated. The flap depths obtainable are 130 µm/160 µm/180 µm. It has a low vacuum mode which prevents any possible compromise of the retinal vascular flow.

Figure 6.5. Moria One reusable microkeratome

Moria One Use—Disposable

The basic principles of its working are similar to that of the basic model, i.e. Moria One except, that it consists of a one piece plastic molded head with one blade inserted which is not amenable to removal (Fig. 6.6). The heads are available for 160 or 180 µm cut and are powered by the same turbine as the one with a reusable head at the rate of 15,000-rpm oscillation.

Figure 6.6. Moria One Use Disposable microkeratome

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Figure 6.8d. Amadeus blade holder

There are separate motors for suction and blade advancement. The suction can be reduced/turned off for reverse pass due to a new software upgrade, which has been incorporated. If the suction is broken, it stops cutting and advancing.

MK2000 Keratome System

This is being supplied by Nidek. It is fully automated and comes as a one piece design for one-handed operation (Fig. 6.9). An audible vacuum indicator is there which makes the surgeon aware of the status of the vacuum. It incorporates two separate motors. One provides a high cutting blade oscillation frequency (18000 cuts). The second motor controls the blade advancement to create a smooth incision. A low profile design allows the tonometry measurements and visualization. The constant oscillation speed is 7,000 rpm which allows for cutting of the smooth flap with diameters of 8.5 and 9.5 mm and depths of 130 µm/160 µm/180 µm. There is complete visualization of the flap when it is being cut.5–7

It has a sliding guide around the suction ring, and the ring itself has dual suction ports that provide continual vacuum readings and consistent pressure measurement.

Figure 6.9. Nidek MK 2000 keratome system

Microkeratomes 63

Schwind Microkeratome

The Schwind microkeratome is produced by Herbert Schwind and has been designed and developed by Hoffmann and Seiler. The device comes as a single unit with accompanying power pack and foot controls. The microkeratome blade is reusable and is made up of sapphire. Each blade can be used approximately for 400 cuts. The angle of contact of the blade with the cornea is 0 degree as compared to 26 degree angle of other microkeratomes, which allows for a low oscillation speed (1600–1800 rpm) during the cut. The blade is electrically propelled and its progression is automated. Its movement is straight and harmonic. The progression speed of the blade is 1.33 mm/sec for a total of 6 seconds.

The thickness plate is fixed and only allows corneal cuts of 150 mm depths. Both anterior and posterior parts of the plate are transparent and the surgeon can directly view the action of the blade on the corneal tissue during the entire procedure.

The vacuum system of the unit contains two suction rings. The rings are fixed and non-adjustable. One ring fixes the eyeball in the peripheral cornea and the other stabilizes the corneal flap during the incision

The electrical motor system of the device is situated in the instrument’s console and two metal drive cables transmit the advancing and oscillatory movements of the blade. This microkeratome cuts a 150 µm thick flap of 9 mm diameter with a 0.5 mm hinge.

The disadvantages of this keratome are the marked vibrations of the instrument, the low oscillation speed of the blade and the use of metal cables to transmit power.

Carriazo-Pendular Microkeratome

This third generation microkeratome has a ball shaped surface with a pendular movement. It is marketed by Schwind Eye-tech-solutions. The pendular movement distributes the pressure mainly to the centre of the eye and protects the corneal centre during the cut (Fig. 6.10).

The size of the suction ring is 19 mm and it can be used in deep set eyes and eyes with small

Figure 6.10. Carriazo-Pendular microkeratome

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palpebral apertures. The hinge can be placed at any position. There are two separate motors, one for the pendular motion and the other for blade oscillation. It has an integrated mechanical stop and there are no permanent internal gears in the cutting head.

Turbokeratome (SCMD Microkeratome)

Under the aegis of SCMD Ltd. this turbine microkeratome has been developed by John Livecchi. The microkeratome head is fixed and does not have a thickness plate. The microkeratome produces 130–150 µm flap thickness. There is a bifaceted blade made up of metal. The angle of attack on the cornea is 20 degrees and its oscillating cycles range from 10,000 to 24,000 rpm, although the recommended oscillation speed of operation is 13,800 rpm. The direction of blade movement is sideways.

The microkeratome is independent of electrical power and a turbine with nitrogen protoxide propulsion powers the oscillations of the blade and it does not have an automated progression system and is advanced manually by the surgeon.

A digital micrometer with adjustment screws between the handle and the head of the microkeratome permits the surgeon to set the stop point and therefore determine the length of the cut.

The unit has multiple suction rings (four) and can create flaps of varying diameter and there are four stop rings that give varying hinge dimensions.

Innovatome

This microkeratome has been developed by Innovative Optics Inc. It is a lightweight, molded plastic microkeratome, weighing only 37 gm on the eye. It has an automated advancement system and is driven by a single flexible cable. There are no gears or mechanical assemblies.

The suction ring is integrated with a unique port chamber design placed nasally. The pneumatic fixation ring is integrated in the device and is mechanically grooved to provide infinite points of suction. The unit has a disposable steel blade that is electrically driven and has a oscillation speed of 12,000 rpm. It allows the creation of either horizontal or vertical flaps the diameter of which ranges from 8.5 mm to 10 mm and depths are of 170, 190 or 220 µm.

A clear sapphire applanator is present which allows the surgeon to directly view the operative field so that the surgeon can predict the location of hinge.

Meditronic Solan Flap Maker Disposable Microkeratome

This microkeratome is being manufactured and distributed by Refractive Technologies Inc, Cleveland, Ohio.

The device comes as a preassembled, single-use, molded plastic unit and is completely disposable (Fig. 6.11). It does not have any gears and is driven by flexible shafts that provide a uniform motion of the microkeratome. It has a metal blade made from surgical stainless steel with an oscillation speed of

Microkeratomes 65

Figure 6.11. Flap maker disposable microkeratome

12,500 cycles per minute. It is driven across the cornea at 6.8 mm per second and only oscillates in the forward motion. The resection depth is variable from 160 to 220 µm and the flap produced has a diameter of 10.5 µm. The unit is made of injection-molded polycarbonate and allows the surgeon to directly visualize the operative field.

Clear Corneal Molder

Dr Ricardo Guirnaraes of Brazil has developed this microkeratome for use in LASIK. It comes as a single-piece integrated instrument unit that includes the head with a dual axis motor, the handle, the suction ring and the plate. It has a diamond or steel blade which is powered by an electrical motor and has an oscillation rate of 12,000 per minute with a 0 degree angle of attack on the cornea. The diameter and the thickness of the corneal flap cut by the device can be varied. Only one pneumatic fixation ring is present and the height is adjustable in relation to the blade.

It also has a transparent surface, which allows the surgeon to directly visualize the operative field during the surgery. The blade movement can be stopped at a preset point with a lever on the handle of the microkeratome, which allows both free caps or hinged flaps to be obtained.

ML MICROKERATOME (A AND M)

The Med-Logics microkeratome may be automated (A) or manual (M). It is made up of a titanium hand piece and uses stainless steel blades to create the flap (Figs 6.12a and b). The blade angle is 24 degrees, the oscillation frequency varies between 9000 and 15,000 oscillations per minute and the rate of advancement of the blade is 3.5 to 5.0 mm/sec. The diameter of the flap created by this microkeratome is between 8 mm and 10 mm and the flap orientation is variable. Two suction rings sizes are provided and the depth of the flap created is 160 µm or 180 µm.

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MICRATOME ADVANCED REFRACTIVE INSTRUMENTATION

The MICRA ACRI microkeratome is a manual instrument. The hand piece is made up of titanium or steel.

Figure 6.12a. Med-Logics microkeratome

Figure 6.12b. Med-Logics console

A stainless steel blade cartridge is used as the cutting mechanism and the blade angle is 25 degrees. Nitrogen gas is used as the power source and the oscillation speed of the blade is 15,000 oscillations per minute. A universal suction ring is provided and the depth of the flap can be 130, 160 or 200 µm. The flap diameter is variable up to 10 mm but the flap orientation is fixed.

Paradigm K-tome

This microkeratome has one size, which fits all suction rings. There are two microkeratome heads—one to treat myopia and the other to treat hypermetropia. The speed of oscillation is 12,000 revolutions per minute. It creates nasal hinges. Visualization during cutting of the cornea is possible. There are separate motors for blade excursion and the suction. A break in the suction automatically stops the excursion of the microkeratome.

It has an etched sapphire applanation plate. There are dual suction ports. There are no gears and due to the high walls of the suction ring the speculum may not be required.

Microkeratomes 67

BD K-3000 Microkeratome

The Becton Dickinson K-3000 microkeratome comes as a pre-assembled device with corneal visualization during the flap creation. The one-piece suction ring is composed of titanium, and fixation is achieved with a 360-degree suction port and a special vacuum system. The three-point gearless guiding system reduces sticking. The 9-mm ring holds three applanation sizes, 8.5 mm, 9 mm, and 9.5 mm and the 10-mm ring holds three applanation sizes, 9.5 mm, 10 mm and 10.5 mm. Recently the newer model BD K-4000 has been launched (Figs 6.13a and b). New safety modifications introduced with the K- 4000 model are real-time monitoring of the system and automatic preoperative testing of the motors and the blade.

Figure 6.13a. Becton Dickinson K- 3000 microkeratome

Figure 6.13b. Becton Dickinson K- 4000 microkeratome

VISIJET HYDROKERATOME

This keratome uses a Water jet technology to create a cleavage in between the corneal lamellae. This is accomplished by fissuring and breaking the collagen bonds between the corneal lamellae while pre-serving the integrity of the lamellae and the keratocytes so that they are not actually cut. Hence this procedure is less traumatic and much safer as compared to the mechanical microkeratomes, which cut across the corneal tissues.

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The anticipated advantages of the hydrokeratome are a decrease in epithelial ingrowth, irregular astigmatism, haze, regression and flap or suction related complications.

The Visijet hydrokeratome uses a continuous beam of ultrahigh pressure saline that is only 36 microns in diameter, to cut a flap across the cornea (Fig. 6.14). The key to the hydrokeratome’s success is the extreme high pressure (over 15,000 psi) combined with a tightly collimated water jet beam. Under these “ultrafluidic conditions” the water molecules leave the orifice of the instrument at a speed in excess of 800 mph and take on almost metallic properties.

A hand piece translates the water jet across the cornea and the angle of attack of the water beam is 0 degree. The surgeon depending on the selected hinge length and flap diameter preprograms the end point of water jet operation.

The flap thickness can be varied from 100 to 200 microns, depending on the thickness plate used and the diameter ranges from 8 to 11 mm.

The applanating surface is made up of lexan, a special plastic and has a diameter of 12 mm. The

Figure 6.14. Visijet hydrokeratome

Table 6.1: Microkeratomes: desi

Table 6.2: Microkerotomes: Functional aspects

surface is transparent and the surgeon has a full visualization of the visual axis at all times.

LASER MICROKERATOME

The laser microkeratome is based on the newer technology. The INTRALASE Femtosecond Laser Microkeratome is an example of laser keratome.

The Femtosecond laser pulses are produced by a solid state, Nd:Glass laser, operating at 1.06 nm wavelength and 450 femtosecond pulse duration. The system consists of a laser oscillator, a pulse stretcher, a regenerative amplifier, and a pulse compressor. The oscillator is mode-locked by a solidstate saturable absorber and produces a train of 250 femtosecond pulses at a repetition rate of 120 MHz. Pulses from the output of the oscillator are selected at a few KHz repetition rate and stretched to a 60 picosecond pulse duration. The pulse is then amplified in a diode-pumped regenerative amplifier and then recompressed to 450 femtosecond pulse duration. Laser energy can varied from 1 to 25 m j.

The laser microkeratome is used as an intrastromal cutting tool based on picosecond intrastromal photodisruption. It causes separation and removal of a small amount of stromal collagen from within the cornea by focusing highly transmissive infrared laser light through the cornea. Each pulse creates a micro-cavitation, which are few microns in size. These pulses are delivered with a computer controlled scanning system.

Pulsion Femtosecond Laser

This creates a 3-micron spot size, which creates the flap. The hinge position may be temporal, nasal or superior. The flap diameters created may be 8.0/ 8.5/9.0/9.5 mm and the flap thickness may be 150/ 160/170/180 µm. These laser pulses are delivered in close proximity of each other in a spiral pattern and the uncut region of the flap is preprogrammed to fashion the hinge.

The main advantages of this technique are the precision and reproducibility of the laser in producing flaps of uniform thickness and the smoothness of the flap interface.8,9

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Suction rings and the cutting blades are also not required in this procedure. Currently, the limitations of this laser technology are the small flap diameter, poor centration, increased intraoperative time and difficulty in dissection. Research is on to develop a solid-state ultraviolet laser, which can be, used both for cutting the flap and intrastromal ablation.

REFERENCES

1.Barraquer JI. Basis of refractive keratoplasty. Arch Soc Amer Oftal Optom 1967:6–21.

2.Barraquer JI. Keratomileusis para la correccion de miopia e hipermetropia. Ann Institute Barraquer de America 1964; 5:209–29.

3.Knorz MC, Liermann A, Wiesinger B, Seiberth V, Liesenhoff H. [Correction of myopia using laser in situ keratomileusis (LASIK)] Klin Monatsbl Augenheilkd 1996; 208(6):438–45. German.

4.Ufret-Vincenty RL, Jiunn-Liang Chen R, Azar DT. Corneal flap displacement and drift in LASIK: comparison of Hansatome and Automated Corneal Shaper microkeratomes. Am J Ophthalmol 2002; 134(5):701–06.

5.Arbelaez MC. Nidek MK 2000 microkeratome clinical evaluation. J Refract Surg 2002; 18(3 Suppl):S357–60.

6.Naripthaphan P, Vongthongsri A. Evaluation of the reliability of the Nidek MK-2000 microkeratome for laser in situ keratomileusis. J Refract Surg 2001; 17(2 Suppl): S255–58.

7.Schumer DJ, Bains HS. The Nidek MK-2000 microkeratome system. J Refract Surg 2001; 17(2 Suppl):S250–51.

8.Sugar A. Ultrafast (femtosecond) laser refractive surgery Curr Opin Ophthalmol 2002; 13(4):246–49.

9.Ratkay-Traub I, Juhasz T, Horvath C, Suarez C, Kiss K, Ferincz I et al. Ultra-short pulse (femtosecond) laser surgery: initial use in LASIK flap creation. Ophthalmol Clin North Am 2001; 14(2):347–55.

7

LASIK Ancillary Instruments and Operating

Environment Variables

Rakesh Ahuja, Jeewan S Titiyal

The basic equipment required for LASIK are a micro keratome and excimer laser machine. However, several other instruments are required to safely perform this surgery. These instruments are categorised in Table 7.1.

These instruments are required for the exposure of the globe, marking of cornea and safe handling and repositioning of the corneal flap.

Instruments for Exposure

Eye Speculum

The eye speculums used for LASIK are of various types (Fig. 7.1). A wire lid speculum provides excellent exposure of the eye. The wire design is preferred over the solid blade type since it does not interfere with placement of the suction ring and excursion of the microkeratome. Lieberman aspirating eye speculum (Fig. 7.2), has an adjustable mechanism. The open wire blades are designed to retain the surgical drape under the eyelids. Suction allows continuous aspiration of fluids for a debris free stroma, which can interfere with laser ablation.

Table 7.1: Ancillary Instruments for LASIK

Instruments for exposure

Eye Speculum

Instruments for marking the cornea

LASIK Corneal Markers

Barraquer Applanation tonometer

Instruments for Flap management

Flap elevator and repositor

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Irrigating cannula

Cellulose Sponges and LASIK drain

Flap protector

Instruments for Re-surgery

Flap edge locators

Flap forceps

Ultrasonic Corneal Pachymeter

Operating room instruments

Air purifier with ionizer

Digital Thermo-hygro-meter

Instruments for Marking the Cornea—LASIK Markers

Accurate marking of the cornea is most important for proper flap centration, flap alignment and flap repositioning after excimer laser ablation. A proper alignment guards against inadvertent flap folds and iatrogenic astigmatism due to improper placement. Moreover, the markings are invaluable in proper

Figure 7.1. Wire speculum

Figure 7.2. Liebermann Temporal aspiration speculum—Six ports on each blade allow continuous aspiration for a debris free stroma

LASIK Ancillary instruments and operating 75

replacement of a free cap. These markers are dipped in 1 percent gentian violet and then placed on the cornea. Various designs available attempt to provide a unique marking pattern to minimize any errors on the part of the surgeon.

1.Optic zone corneal marker: It can be used to mark the cornea before microkeratome cut (Fig. 7.3). The ring gives better alignment of the flap. Marking the cornea at three meridians, 3, 6, 9 O’clock is used. In the event of free cap, this

Figure 7.3. Optic zone corneal marker

may provide better guideline for replacement of the flap.

2.LASIK flap marker: has an optical zone 8 mm with 3 marking lines which are asymmetrical to ensure correct placement of corneal flap.

3.Lavery LASIK marker: It has an optical zone of 8 mm, with five marking lines which are asymmetrical, to ensure right placement of corneal flap (Fig. 7.4). It has an optical centre sight for surgeon’s convenience.

Figure 7.4. Lavery LASIK marker

4.Antzoulatos LASIK marker: It has an optical zone 8 mm with half circles (Fig. 7.5). It is used for guarding against flap displacement, flap centration and to avoid placing a free flap upside down.

Figure 7.5. Antzoulatos corneal marker

LASIK Ancillary instruments and operating 77

microkeratome for making the flap, IOP should be at least 60 to 65 mm Hg. This is important since a lower IOP may result in higher risk of flap complications, like thin flap, buttonholed flap, or even perforation of the cornea.

Instruments for Flap Management

1.LASIK Flap elevator spatula: These are used for lifting the flap after the microkeratome cut and also for replacing the flap after the excimer ablation (Fig. 7.8). These are imperative for LASIK enhancement surgery to relift the flap.

Figure 7.8. LASIK flap spatula

a.Fukasaku LASIK spatula: It has rounded anterior and flat posterior surface with dissecting tip and is used for lifting and dissecting the corneal flap (Fig. 7.9).

Figure 7.9. Fukasaku LASIK spatula

b.Guimaraes LASIK spatula has gently curved, bi-convex, semi-sharp edges (Fig. 7.10).

Figure 7.10. Guimaraes LASIK spatula

c.Alio-Rodriguez dual LASIK Spatula: It has dual 12 mm long 0.25 mm diameter arms (Fig. 7.11).

Figure 7.11. Alio-Rodriguez LASIK spatula

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d.Maddox LASIK spatula: It combines a flat spatula and a cylindrical spatula and is used for elevating and repositing the flap (Fig. 7.12).

Figure 7.12. Maddox LASIK spatula

2.Irrigating cannula: It is used for irrigating the interface of LASIK flap and stroma. It helps to dislodge any particles from the corneal interface. Multidirectional cannula help to irrigate the interface in one single sweep. A range of designs is available with openings ranging from 2 to 8 per cannula.

a.Spatulated LASIK cannula: It has a flattened spatulated tip with end opening of 26 gauge (Fig. 7.13).

Figure 7.13. Spatulated LASIK cannula

b.Fukasaku LASIK cannula with a low profile tip and an end opening of 23 gauge (Fig. 7.14).

c.Gimbel LASIK fountain cannula has a smooth bullet shaped tip with a single center port of

Figure 7.14. Fukasaku LASIK cannula

25 gauge for directing fluid toward the superior hinge.

d.Banaji LASIK Cannula has a bullet shaped tip and 6 ports of 25 gauge size for multi-directional irrigation (Fig. 7.15).

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Figure 7.15. Banaji LASIK cannula tip

e.Brierley LASIK cannula has a closed spatulated tip with 6 ports with a size of 25 gauge for multi-directional irrigation.

f.Carter LASIK cannula has an end opening flattened tip of 25 gauge.

g.Buratto LASIK cannula has one front and two side ports. These are designed for equal flow in all the three directions (Fig. 7.16).

Fig 7.16. Buratto LASIK Cannula tip

h.Vidaurri LASIK cannula is double-armed with 8 irrigating ports in size of 25 gauge.

i.Cobra LASIK cannula has 6 ports for multi-directional irrigation with a size of 23 gauge (Fig. 7.17).

Figure 7.17. Cobra LASIK cannula tip

j.Gimbel LASIK polishing cannula has a flattened textured tip in a size of 30 gauge. It is used for dislodging and irrigating particles from the corneal interface (Fig. 7.18).

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Figure 7.18. Gimbel LASIK polishing cannula

3.Cellulose sponges and LASIK drain: Cellulose sponge spears used in LASIK should be of high quality and should not leave behind any remnants like fibres. These are provided sterile for single use and should be disposed of after surgery.

i.Merocel spear sponges (Xomed, Jacksonville FL) It is made of lint free PVA with a triangle shaped spearhead set on a malleable, polypropylene handle. The sponges are soaked in proparacaine 0.5 percent solution for anaesthetizing the conjunctival fornices. A dry spear is used to clean any debris from the conjunctival surface, wipe excessive moisture from corneal surface in between ablation and to remove excess moisture from borders of replaced flap for proper adherence to the stromal bed. A wet sponge is used to keep the reflected flap hydrated, wipe the corneal stromal bed and also to iron back the flap on to the bed after ablation is complete. This ironing is done from the side of the hinge towards the non-hinge area till the flap is free of striae and properly adherent to corneal stromal bed.

ii.LASIK drain: It is made of thin synthetic PVA sponge and completely encircles the cornea. It is used for preventing excessive hydration of stromal bed during laser ablation,

a.Chayet LASIK Drain: It has a central 10-mm opening and is designed for nasally hinged flaps (Fig. 7.19).

Figure 7.19. Chayet LASIK drain

b.Gimbel-Chayet LASIK drain: It has a central opening of 9.5 mm and is designed for both nasally as well as superiorly hinged flaps (Fig. 7.20).

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Figure 7.20. Gimbel-Chayet LASIK drain

4.Flap protector: A flap protector shields the everted flap from inadvertent ablation by the excimer beam, which is an iatrogenic complication (Fig. 7.21). A corneal paper shield fashioned using scissors may be used for the same purpose,

a. Buratto LASIK flap protector: It is used for retracting and protecting nasally hinged

Figure 7.21. LASIK flap protector

corneal flaps (Fig. 7.22). Buratto flap protector is also available with blades angled at 15° for retracting and protecting superiorly hinged corneal flaps.

Figure 7.22. Buratto LASIK flap protector

b.Mannis-Buratto LASIK flap protector: It has blades angled 45° used for retracting and protecting superiorly hinged corneal flaps (Fig. 7.23).

Figure 7.23. Mannis-Buratto LASIK flap protector

c.Rowen combination instrument: It has a LASIK flap protector on one side and a spatula on the other side. It is used for protecting the flap as well as a spatula (Fig. 7.24).

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Figure 7.24. Rowen combination instrument

Instruments for Re-LASIK

1.Flap edge locators

a. LASIK flap manipulator: It has a delicate, smooth polished olive shaped tip (Fig. 7.25). This tip is used to gently depress the cornea to locate the flap edge. Once located, the olive

Figure 7.25. LASIK flap manipulator

tip can then be used to engage the edge and slide it around the rim to partially open the flap.

b.Fox LASIK Flap Edge Dissector: It has a three pronged tip which is used for finding the edge of flap in LASIK enhancement surgery (Fig. 7.26).

Figure 7.26. Fox LASIK flap edge dissector

c.Maddox LASIK spatula: It combines a flat spatula and a cylindrical spatula. It is used for elevating and repositing the flap in enhancement surgery.

d.Banaji LASIK flap spatula It has extremely thin duckbill shaped tip at one end curved and the opposite end is angled.

e.Katzen LASIK flap “Unzipper”: It combines a modified sinskey Hook and a biconvex spatula with beveled notches. It is used for lifting and dissecting the corneal flap in enhancement surgery.

2.LASIK flap forceps

LASIK Ancillary instruments and operating 83

a.Collibri, Pierse forceps: These forceps are used for reflecting and repositioning the hinged flap in re-surgery as well as for handling a free cap in case of complete resection.

b.Mendez Multi-Purpose LASIK forceps: It has spatulated jaws and tips with smooth grasping surfaces, vaulted (Fig. 7.27). It may be used for lifting, dissecting and grasping the corneal flap.

Figure 7.27. Mendez multi-purpose

LASIK forceps

c.Fechtner conjunctiva forceps: is very delicate with ring shaped tips having a tying platform (Fig. 7.28).

Figure 7.28. Fechtner conjunctiva forceps tip

d.Buratto LASIK flap forceps: It is disc shaped with serrated jaws for manipulating the flap (Fig. 7.29).

Figure 7.29. Buratto LASIK flap forceps tip

Step by step LASIK surgery 84

Ultrasonic Corneal Pachymeter

Corneal pachymetry is necessary in each case prior to LASIK for determining suitability for surgery. We use the Sono Gage corneal pachymeter to perform ultrasonic pachymetry (Fig. 7.30). It has a 50 MHz transducer with multiple examination modes. Proper vertical placement of the probe onto an anaesthetized cornea gives highly accurate readings of corneal thickness. The readings of corneal pachymetry obtained with ultrasonic method are much more reliable as compared to the Orbscan and Optical pachymetry.

Figure 7.30. Sono Gage corneal pachymeter

Performing intraoperative corneal pachymetry gives the stromal bed thickness from which the flap thickness may be derived by simple subtraction. Thin flaps, less than 100 mm, should preferably not be re-lifted in LASIK retreatment/enhancement procedures. In such cases a second microkeratome cut is made and enhancement done.

Operating Room Environment Variables

Operating room environment, including temperature and more particularly humidity are important controllable parameters for LASIK surgery. The proper laser room environment is critical for optimal laser performance. These variables should be set to the manufacturer’s recommendations for the particular machine. In general, the temperature should be maintained between 18 to 24°C, and the humidity should be kept below 50 percent.

Environmental factors that can affect final LASIK correction include the temperature, humidity and altitude of the laser center, as well as the amount of particulate matter created by plumes.1 Humidity may be more significant than temperature in controlling excimer laser ablation. The corneal stroma can hydrate and swell up after removal of flap, while the light of operating microscope leads to superficial dehydration. Lower levels of humidity are likely to result in a drier stromal bed, which may result in more than intended excimer laser ablation.2

Humidity and temperature should be meticulously measured using manufacturer recommended and certified scientific instruments. The digital thermo-hygro-meter (Fig. 7.31) gives instant digital reading of the temperature and humidity. Both these parameters

LASIK Ancillary instruments and operating 85

should be noted down in LASIK surgical notes for each individual patient. This becomes particularly important when the attempted correction and final outcome in a patient do not match.

The excimer laser optics are highly sensitive to dust and other such particles. The Air - purifier with ionizer is used for filtering air and removing particles from the operating room environment. It removes any particulate matter down to a size of 0.1 mm, including the bacteria. An inbuilt activated carbon filter helps to remove any odors. The ionizer device releases negatively charged ions which help

Figure 7.31. Digital thermo-hygro- meter

reduce the static electricity created by the computer screen.

REFERENCES

1.de Souza IR, de Souza AP, de Queiroz AP, Figueiredo P, Jesus RS, kara-Jose N. Influence of temperature and humidity on laser in situ keratomileusis outcomes. J Refract Surg. 2001; 17(2 Suppl):S202–4.

2.Titiyal, JS, Alka R, Balasubramanya R, Sharma N, Vajpayee RB, Singh R. Effect of operating room environmental factors (Temperature and Humidity) on results of LASIK. ESCRS poster presentation, Nice 2002.

Section 3

Surgical Technique